Measurements of dilepton channels at LHCb

Plews, Jonathan (2022). Measurements of dilepton channels at LHCb. University of Birmingham. Ph.D.

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Abstract

Measurements of the Drell-Yan cross-section provide insight into the structure ofthe proton. Measurements are made at LHCb, via the dimuon channel, as a double differential cross-section with respect to dimuon mass and rapidity, and with respectto dimuon mass and transverse momentum in the ranges 4 < $m_{\mu\mu}$ < 120GeV, 2.5 < $y$ < 4.5 and 1< $p_{T}$ < 500GeV. Dimuon candidates are selected from 1.63 fb^{-1} of data taken at LHCb in 2016 and fit as a function of minimum muon $\sqrt{\chi^{2}_{IP}}$ using templates for components of the signal and the relevant backgrounds. A search for the lowest spin-triplet state of true muonium ( $\mu^{+}\mu^{-}$ ) is also proposed. True muonium offers an opportunity to test standard model physics in a purely muonic system. It is suggested that decays of $TM \rightarrow e^{+}e^{−}$ could be detected at LHCb, produced from the decays of $\eta\rightarrow\gamma^{*}\gamma$ , where $\gamma^{*}$ mixes with $TM$ . Two searches are proposed, an inclusive search where only the dielectron pair is selected and an exclusive search where the photon is also selected and the $\eta$ meson is reconstructed. It is shown that in order to discover true muonium to $5\sigma$ significance, LHCb would be required to achieve reconstruction efficiencies of $\varepsilon_{e^{+}e^{-}}$ > 20% and $\varepsilon_{\gamma e^{+}e^{-}}$ > 12%, within the fiducial acceptance.